This invention is directed to a method for making a composite electrode structure for use in crossed-field switch devices.
Crossed-field electrical discharge devices were primarily laboratory curiosities, until recent developments having shown that they are capable of carrying high direct currents and interrupting against high voltages. This capability has resulted in their design into a number of circuit breakers. In such circuit breakers, the crossed-field devices become crossed-field interrupting devices which perform the function of interrupting direct current to result in increasing circuit breaker impedance. Prior patents which can use suitable crossed-field switch devices as their switching elements in circuit breaker environments include K. T. Lian U.S. Pat. No. RE 27,257; K. T. Lian and W. F. Long U.S. Pat. No. 3,641,358; M. A. Lutz and W. F. Long U.S. Pat. No. 3,660,723. These illustrate the manner in which a crossed-field switch device can be used.
Two patents which illustrate particular structure of a crossed-field switch device are G. A. G. Hofmann and R. C. Knechtli U.S. Pat. No. 3,558,960 and M. A. Lutz and R. C. Knechtli U.S. Pat. No. 3,638,061. These patents discuss the maintenance of pressure in the interelectrode gap during conduction. Furthermore, G. A. G. Hofmann U.S. Pat. No. 3,604,977 and M. A. Lutz and G. A. G. Hofmann U.S. Pat. No. 3,678,289 discuss the management and control of the off-switching of crossed-field switch devices by control of the magnetic field. Continuing improvements are being made to enhance the voltage and current capabilities, as well as life and reliability of the crossed-field switch devices.
The electrode surfaces, particularly the cathode surface which is exposed to high intensity discharge in the crossed-field switch device, should be of a material which is resistant to sputtering to maximize tube life, and resistant to the glow-to-arc transition to attain high reliability. These requirements are met by refractory materials. However, the cathode as a whole should have enough mechanical strength to serve as a tube envelope. Furthermore, it should resist eddy currents which are set up by the magnetic field switching, and it should be as economic as possible. These requirements are best met by other than refractory materials.